Communication systems, such as cellular or trunked communication systems, are known to include a plurality of subscriber units and an infrastructure communication center that is typically controlled by a service provider. Depending on the type of system, the subscriber units might comprise cellular telephones or two-way radio devices. Each subscriber unit is fabricated by a particular manufacturer and is assigned a corresponding serial number. The infrastructure communication center is typically connected to a plurality of base sites that provide radio communication channels to the subscriber units. The infrastructure communication center typically includes a home location register (HLR) that is coupled to a switch. As is known, the switch controls subscriber unit access to the radio channels and provides interconnection to the public switched telephone network.
Prior to service activation of a subscriber unit, an employee for the service provider typically allocates a mobile identification number (MIN) for the subscriber unit and stores the identification number in the subscriber unit. The employee also stores the identification number and the corresponding subscriber unit serial number in the HLR. The subscriber identification number enables the subscriber unit to access the particular communication system and is used by the service provider to monitor the amount of service (e.g., air time) provided to the subscriber unit. With this procedure, service is available from the service provider within a nominal activation time period after the user of the subscriber unit requests service activation (e.g., at the point of sale of the subscriber unit). Although this approach is straightforward, access to subscriber unit identification numbers and corresponding subscriber unit serial numbers is readily available to employees of the service provider. Unfortunately, this uncontrolled access has accounted for numerous occurrences of service fraud resulting from the cloning of subscriber units (i.e., copying the identification number and serial number assigned to one subscriber unit into another subscriber unit).
In an attempt to reduce the occurrences of service fraud, two security concepts have been recommended. The first concept has been recommended for the existing United States Digital Cellular (USDC) Systems based on Telecommunications Industry Association/Electronics Industry Association Interim Standards 54 and 95 (TIA/EIA IS-54 and IS-95). This technique requires the service provider to send an authorization code to the user of the subscriber unit via the United States Postal Service. Upon receipt of the code, the user enters the authorization code into the subscriber unit, provided the subscriber unit has a keypad, to activate service. Although this approach offers adequate security, it imparts an unwelcome burden on the user of the subscriber unit. Further, this technique includes an inherent delay between the request for service and the activation of service due to the mail delivery of the authorization code.
The second concept is currently being used in the Groupe Special Mobile (GSM) Pan European cellular communication system (also denoted the Global System for Mobile communication). This approach requires the user of a subscriber unit to insert an authorization card into a card reader that accompanies the subscriber unit prior to use. The authorization card includes the subscriber unit's identification number and a secure key. The secure key is a digital word that further identifies the subscriber unit and is typically used by the service provider to confirm a subscriber unit's system access privileges. Accordingly, this technique imparts the burden of requiring the subscriber unit's user to carry an authorization card whenever the user intends to utilize the subscriber unit. Further, this approach requires that the additional card reader hardware be purchased in conjunction with the subscriber unit, thereby raising the cost of owning the subscriber unit.
Therefore, a need exists for a method of secure messaging in a communication system that provides for secure use of a subscriber unit's identification number and secure key without imparting any additional burden on the subscriber unit's user, without causing undue delays in service activation, and without requiring additional hardware to accompany the subscriber unit.